Magnetron device



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The present invention relates to improved magnetron devices and particularly to improved cathode structures for injection type magnetrons of a type well suited for anode voltage tuning applications.

In US. Patent 2,774,039, Peters et al., dated December 11, 1956, there is described and claimed a method and apparatus for tuning a magnetron system over a wide frequency range for varying the anode voltage. As outlined in that patent it has been found that the oscillating frequency of the magnetron system will vary directly with the direct current voltage applied to the anodecathode circuit, if the rate of increase of the high frequency voltage with respect to an increase in the direct current anode-cathode voltage is properly controlled. It is further stated that variation of the high frequency voltage with direct current anode-cathode voltage may be kept within the desired relationship if the anode circuit is heavily and uniformly loaded over the entire tuning range and, at the same time, the number of electrons in the interaction space is suitably limited. The present invention is directed particularly to improved cathode structures which are well adapted for use in injection type voltage tunable magnetrons.

In accordance with the present invention an indirectly heated type of cathode supported in longitudinally displaced relation with respect to the interaction space of the magnetron is provided and is supported from the remote end of the magnetron envelope by the non-emitting portion of the cathode structure. The heater is supported from the end of the envelope which is in proximity to the emitting part of the cathode. A bifilar heater structure is employed to eliminate magnetic effects due to the heater current.

The present invention provides a simple structure which is relatively easily manufactured, conserves heater power and which provides for uniform field patterns in the control and interaction region and at the same time removes the emitting surface from the interaction space and, in this way, eliminates or minimizes the effect of back heating on the number of electrons available in the interaction space.

Further objects and advantages of my invention will become apparent as the following description proceeds, reference being had to the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing, FIGURE 1 is an elevational view in section of a magnetron discharge device embodying my invention, and

FIGURE 2 is a sectional view taken along the line 22 of FIGURE 1.

In the preferred embodiment of my invention illustrated in the drawing the envelope is made up of a plurality of generally cylindrical hollow insulating members 1, 2, 3 and 4 which may to advantage be of ceramic material. In the form illustrated the insulator 4 is generally cup-shaped and is provided in its end wall with small spaced openings 5 and 6 through which the cathode heater supply conductors 7 and 8 extend. These conductors terminate in external terminals 9 and 10 which are bonded to the ceramic member. In the arrangement shown conductors 7and 8 are the opposite ends of the conductor which forms the hollow cylindrical bifilar heater coil 11 and support the heater coil 11 concentrically within the cathode sleeve, as will be described. The adjacent edges of the insulators 1 and 2 are separated atent 2,997,524 Patented Aug. 22, 1961 ice internally of the envelope a support for a cylindrical array of spaced anode sections or digits 13. In a similar manner, terminal 14 is sealed between adjacent ends of insulators 2 and 3 and provides the support for a similar cylindrical array of anode sections 15 which are supported in alternate or interdigital relation with respect to the sections 13 supported from the terminal 12.

A generally frustoconical control electrode 16 having the smaller end thereof adjacent the lower end of the anode structure is supported from an annular terminal 17 sealed between adjacent ends of insulators 3 and 4. The upper end of insulator 1 and of the envelope of the device are closed by a disk 18 which supports the cathode structure of the device. The cathode includes a molybdenum or tungsten support 19 bonded to the plate or disk 18 and includes a non-emitting cylindrical hub 20, which may be integral with support 19, positioned concentrically with the cylindrical array of anode sections supported from terminals 12 and 14 and a hollow cylinder 21, preferably of nickel or similar material, supported concentrically within the frustoconical control electrode 16 and longitudinally displaced from the interaction space between the non-emitting cathode 20 and the :anode sections 13 and 15. The cathode is supported from the non-emitting portion 20 by means of a cylindrical collar 22 and encircles the heater element 11. The emitting cylinder, which is closed at its upper end by 'a heat shield, is spaced from the solid hub 20 so that the heat transfer to the supporting hub is essentially limited to the limited cross section of the sheetmetal or foil cylindrical support 22.

In accordance with the preferred embodiment of the present invention the ceramic parts 1, 2, 3 and 4 are of a forsterite ceramic having *a temperature coeflicient of expansion corresponding closely to that of titanium. Such a ceramic may include magnesium oxide (MgO), aluminum oxide (A1 0 and silicon dioxide (SiO in weight percentages respectively of approximately 52, 6 and 42. The anode terminal members 12 and 14 are preferably made of copper or similar metal having similar good heat transfer characteristics to assist in dissipating the heat generated at the anode sections. While the coefficient of thermal expansion of copper will not match that of the same ceramic as used for matching the expansion of the titanium, a certain amount of mismatch is permissible, particularly with copper, since copper yields to partially relieve the stresses resulting from bonding together parts having different expansions. Also in the construction illustrated the ceramic members are sealed to opposed equal areas of the metal members and this also minimizes difficulties which might otherwise result from the unequal expansion coeflicients of the copper and ceramic parts.

In accordance with a preferred method of fabricating the present invention, the bonds between all of the metal and ceramic parts are made during one heating step. This is accomplished by utilizing titanium brazing shims between the copper terminals 12 and 14 and the ceramic members and copper, nickel or similar brazing shims between the ceramic members and the titanium members 9, 10, 17 and 18. In the manufacture of the device, the parts are assembled in a stack and the: assembly is heated to a temperature sufiicient to alloy the shims with the parent metal of the higher melting combination, the titanium nickel seals. At this temperature the copper titanium seals will have become copper rich so as to have maximum ductility. The entire envelope seals at a single temperature. Thus, it is possible to take advantage of the desirable characteristics of titanium with respect to certain of the seals and also with respect to 3 its gas absorbing action in the device. At the same time the good heat transfer and electrical characteristics of the copper terminals associated with the anode facilitate the production of a high frequency device capable of handling. amounts of power greater than would be possible were the anodes made of a metal, such as titanium, having an expansion characteristic matching that of the ceramic. The particular arrangement of the cathode provides a relatively simple structure in which the amount of heat lost to the non-emitting hub is minimized and at the same time the support from a single end of the device facilitates manufacture. The smooth exterior surface provides relatively smooth voltage gradients and facilitates the injection of electrons to the interelectrode space.

The interdigital structure is Well suited to voltage tuning and the injection system renders it possible to readily control the number of electrons in the electrode space, another condition utilized in the voltage tuning in accordance with the invention of the Wilbur and Peters patent.

While I have described a particular embodiment of my invention it will be apparent to those skilled in the art that changes and modifications may be made without departing from my invention in its broader aspects. I aim, therefore, in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric discharge device of the magnetron type comprising an envelope, an anode structure within the envelope including a cylindrical array of anode sections facing a central cylindrical lopening, a cathode structure supported from one end of said envelope and including a cylindrical non-emitting portion within said cylindrical opening, a hollow substantially continuous cylindrical portion providing a cylindrical emitting surface supported from said non-emitting portion and longitudinally displaced from said anode in the direction of the other end of said envelope, a heater element positioned within said hollow emitting portion and including a supply conductor sealed through said envelope and a heat shield in said hollow cylindrical portion between said heater element and said non-emitting portion.

2. An electric discharge device of the magnetron type comprising an envelope, an anode structurue within the envelope including a cylindrical array of anode sections facing a central cylindrical opening, a cathode structure supported from one end of said envelope and including a cylindrical non-emitting portion within said cylindrical opening, a hollow substantially continuous cylindrical portion providing a cylindrical emitting surface supported from said non-emitting portion and longitudinally displaced from said anode in the direction of the other end comprising an envelope, an anode structure within the envelope including a cylindrical array of anode sections facing a central cylindrical opening, a cathode structure supported from one end of said envelope and including a solid cylindrical non-emitting portion within said cylindrical opening, a hollow cylindrical portion provding a substantially continuous cylindrical emitting surface supported from said non-emitting portion and longitudinally displaced from said non-emitting portion in the direction of the other end of said envelope, a transverse wall extending across said hollow portion in spaced relation to the end of said solid portion to provide a heat shield and a heater element positioned within said hollow portion on the side of said wall remote from said non-emitting portion including supply conductors sealed through the opposite end of said envelope and supporting said heater element.

4. An electric discharge device of the magnetron type comprising an envelope, an anode structure within the envelope including a cylindrical array of anode sections facing a central cylindrical opening, a cathode structure supported from one end of said envelope and including a cylindrical non-emitting portion within said cylindrical opening, a hollow cylindrical portion providng a substantally continuous cylindrical emitting surface supported from said non-emitting portion and longitudinally displaced from said anode in the direction of the other end of said. envelope, a control electrode surrounding said emitting surface for controlling the supply of electrons to the space between said non-emitting portion and said array of anode sections, a heater element positioned Within said hollow portion and including a supply conductor sealed through the opposite end of said envelope and sup porting said heater element and a heat shield extending across said hollow cylindrical portion between said heater element and said non-emitting portion.

References Cited in the file of this patent UNITED STATES PATENTS 2,412,372 Usselman Dec. 10, 1946 2,585,741 Clogston Feb. 12, 1952 2,774,039 Peters Dec. 11, 1956 2,810,095 Peters Oct. 15, 1957 2,810,096 Peters Oct.15, 1957 2,826,719 Donal Mar. 11, 1958 2,930,933 Griflin Mar. 29, 1960 

